Process for the production of (meth)acrylic acid and derivatives and polymers produced therefrom

ABSTRACT

A method of extracting (meth)acrylic acid from an aqueous reaction medium into an organic phase in contact therewith is described. The aqueous reaction medium is formed from at least one base catalyst and at least one dicarboxylic acid selected from maleic, fumaric, malic, itaconic, citraconic, mesaconic, and citramalic acid or mixtures thereof in aqueous solution and contains the base catalyzed decarboxylation products of the base catalyzed reaction. The method includes either the addition of at least one of the said dicarboxylic acids and/or a pre-cursor thereof to the aqueous reaction medium to enhance the solvent extraction of the (meth)acrylic acid into the organic solvent or maintaining the level of base catalyst to dicarboxylic acid and/or pre-cursor at a sub-stoichiometric level during the extraction process. The method extends to a process of producing (meth)acrylic acid, its esters and polymers and copolymers thereof.

This application is a divisional of U.S. patent application Ser. No.13/984,473, filed on Oct. 16, 2013, which is a national stage ofInternational Application No. PCT/GB2012/050272, filed Feb. 8, 2012,which claims priority to GB 1102249.8, filed Feb. 9, 2011 and GB1110741.4, filed Jun. 24, 2011, each of which is incorporated byreference in its entirety.

The present invention relates to a process for the production of(meth)acrylic acid (meaning herein acrylic acid or methacrylic acid) orderivatives such as esters thereof by the decarboxylation of selectedacids in the presence of base catalysts and the extraction of the(meth)acrylic acid product from the reaction medium.

Acrylic acid (AA) and Methacrylic acid (MAA) and their esters,particularly methyl, ethyl and butyl esters, such as ethyl acrylate,butyl acrylate, methyl methacrylate (MMA) and butyl methacrylate areimportant monomers in the chemical industry. Their main application isin the production of polymers for various applications. The mostsignificant polymer applications are for acrylic acid in superabsorbentpolymers, and methacrylate and acrylate esters for surface coatings andfor high optical clarity plastics produced by the casting, moulding orextrusion of polymethyl methacrylate (PMMA). In addition, manycopolymers of AA and its esters and MAA or MMA are used; importantcopolymers are copolymers of MMA with α-methyl styrene, ethyl acrylateand butyl acrylate. Currently AA, MMA and MAA are produced entirely frompetrochemical feedstocks.

Conventionally, MMA has been produced industrially via the so-calledacetone-cyanohydrin route. The process is capital intensive and producesMMA from acetone and hydrogen cyanide at a relatively high cost. Theprocess is effected by forming acetone cyanohydrin from the acetone andhydrogen cyanide: dehydration of this intermediate yields methacrylamidesulphate, which is then hydrolysed to produce MAA. The intermediatecyanohydrin is converted with sulphuric acid to a sulphate ester of themethacrylamide, methanolysis of which gives ammonium bisulphate and MMA.However, this method is not only expensive, but both sulphuric acid andhydrogen cyanide require careful and expensive handling to maintain asafe operation and the process produces large amounts of ammoniumsulphate as a by-product. Conversion of this ammonium sulphate either toa useable fertilizer or back to sulphuric acid requires high capitalcost equipment and significant energy costs.

Alternatively, in a further process, it is known to start with anisobutylene or, equivalently, t-butanol reactant which is then oxidizedto methacrolein and then to MAA.

An improved process that gives a high yield and selectivity and farfewer by-products is a two stage process known as the Alpha process.Stage I is described in WO96/19434 and relates to the use of1,2-bis-(di-t-butylphosphinomethyl)benzene ligand in the palladiumcatalysed carbonylation of ethylene to methyl propionate in high yieldand selectivity. The applicant has also developed a process for thecatalytic conversion of methyl propionate (MEP) to MMA usingformaldehyde. A suitable catalyst for this is a caesium catalyst on asupport, for instance, silica. This two stage process althoughsignificantly advantageous over the competitive processes availablestill nevertheless relies on ethylene feed stocks predominantly fromcrude oil and natural gas, albeit bioethanol is also available as asource of ethylene.

Acrylic acid is conventionally prepared by oxidation of propene which isderived exclusively from oil, gas or coal feedstocks.

For many years, biomass has been offered as an alternative to fossilfuels both as a potential alternative energy resource and as analternative resource for chemical process feedstocks. Accordingly, oneobvious solution to the reliance on fossil fuels is to carry out any ofthe known processes for the production of AA, MMA or MAA using a biomassderived feedstock.

In this regard, it is well known that syngas (carbon monoxide andhydrogen) can be derived from Biomass and that methanol can be made fromsyngas. Several Industrial plants produce methanol from syngas on thisbasis, for example, at Lausitzer Analytik GmbH Laboratorium für Umweltand Brennstoffe Schwarze Pumpe in Germany and Biomethanol ChemieHoldings, Delfzijl, Netherlands. Nouri and Tillman, Evaluating synthesisgas based biomass to plastics (BTP) technologies, (ESA-Report 2005:8ISSN 1404-8167) teach the viability of using methanol produced fromsynthesis gas as a direct feedstock or for the production of otherfeedstocks such as formaldehyde. There are also many patent andnon-patent publications on production of syngas suitable for productionof chemicals from biomass.

The production of ethylene by dehydration of biomass derived ethanol isalso well established with manufacturing plants in, especially, Brazil.

The production of propionic acid from carbonylation of ethanol and theconversion of biomass derived glycerol to molecules such as acrolein andacrylic acid is also well established in the patent literature.

Thus ethylene, carbon monoxide and methanol have well establishedmanufacturing routes from biomass. The chemicals produced by thisprocess are either sold to the same specification as oil/gas derivedmaterials, or are used in processes where the same purity is required.

Thus in principle there is no barrier to operation of the so calledAlpha process above to produce methyl propionate from Biomass derivedfeedstocks. In fact, its use of simple feedstocks such as ethylene,carbon monoxide and methanol rather sets it apart as an ideal candidate.

In this regard, WO2010/058119 relates explicitly to the use of biomassfeedstocks for the above Alpha process and the catalytic conversion ofmethyl propionate (MEP) produced to MMA using formaldehyde. These MEPand formaldehyde feedstocks could come from a biomass source asmentioned above. However, such a solution still involves considerableprocessing and purification of the biomass resource to obtain thefeedstock which processing steps themselves involve the considerable useof fossil fuels.

Further, the Alpha process requires multiple feedstocks in one locationwhich can lead to availability issues. It would therefore beadvantageous if any biochemical route avoided multiple feedstocks orlowered the number of feedstocks.

Acrylic acid is conventionally prepared by oxidation of propene which isderived exclusively from oil, gas or coal feedstocks.

Therefore, an improved alternative non-fossil fuel based route toacrylate monomers such as AA, MMA and MAA is still required.

PCT/GB2010/052176 discloses a process for the manufacture of aqueoussolutions of acrylates and methacrylates respectively from solutions ofmalic and citramalic acids and their salts.

Carlsson et al. Ind. Eng. Chem. Res. 1994, 33, 1989-1996 has discloseditaconic acid decarboxylation to MAA at high temperatures of 360° C. andwith a maximum yield of 70% where a proportion of the acid is present asa base salt, for instance, sodium itaconate. Unfortunately, Carlssondoes not disclose any purification methodology to recover the MAA fromthe reaction medium. Carlsson discloses that the activity for thedecomposition reaction increases with the concentration of the sodiumsalt relative to the free acid. The selectivity falls as theconcentration of itaconic acid is raised in the solution prior todecomposition.

U.S. Pat. No. 4,142,058 discloses the extraction of methacrylic acidfrom acidic aqueous solutions using mixtures of MMA and toluene undercounter current flow. The aqueous phase goes to waste. U.S. Pat. No.3,968,153 discloses the extraction of acrylic and/or methacrylic acidfrom an aqueous phase using methylethyl ketone and xylenes. U.S. Pat.No. 4,956,493 discloses extracting methacrylic acid from its aqueoussolution using a saturated chain aliphatic hydrocarbon having 6 to 9carbon atoms as a solvent. Xylene and toluene are said to beproblematic. EP 710643 uses an organic solvent to extract methacrylicacid from its aqueous solution and treats the organic extract with waterto assist in the removal of close boiling acids citraconic and maleicacid from the extract. U.S. Pat. No. 4,879,412 and JP 193740/1989discuss the treatment of the organic phase with a basic ion exchangeresin and U.S. Pat. No. 5,196,578 discloses a similar process usingamines. The processes are problematic because they introduce additionalimpurities and can lead to by-products that cause polymerisation of themethacrylic acid leading to equipment failure.

Those skilled in the art would realise that the conditions of thesolution generated according to the teaching of Carlsson et al would notbe suitable for subsequent solvent extraction because of the lowconcentration of MAA and the high concentration of base. Basic salts ofAA and MAA have high solubilities in water and very low solubilities inorganic solvents.

Surprisingly, it has now been discovered that AA and MAA can beextracted from an aqueous decarboxylation reaction medium in thepresence of a basic catalyst with a surprisingly improved yield.Furthermore, the extraction process allows the basic solutions afterextraction to be recycled into the decarboxylation reaction so that acontinuous decarboxylation and extraction process to generate AA and MAAfrom di and tri carboxylic acids can be achieved with a single additionof base, such that the base catalysed reaction may be conductedcontinuously.

According to a first aspect of the present invention there is provided amethod of extracting (meth)acrylic acid from an aqueous reaction medium,the aqueous reaction medium being formed from at least one base catalystand at least one dicarboxylic acid selected from maleic, fumaric, malic,itaconic, citraconic, mesaconic and citramalic acid or mixtures thereofin aqueous solution and containing the base catalysed decarboxylationproducts thereof including (meth)acrylic acid and/or (meth)acrylate basesalt, the method comprising the steps of introducing an organic solventto the said aqueous reaction medium for solvent extraction of the(meth)acrylic acid into an organic phase wherein the method ischaracterised in that there is added an additional amount of at leastone of the said dicarboxylic acids and/or a pre-cursor thereof to thesaid aqueous reaction medium to enhance the solvent extraction of the(meth)acrylic acid into the organic solvent.

Preferably, the concentration of (meth)acrylic acid in the aqueous phaseextraction is at least 0.05 mol dm⁻³, more preferably, at least 0.1 moldm⁻³, most preferably, at least 0.2 mol dm⁻³, especially, at least 0.3or 0.4 mol dm⁻³. In a batch reaction, this concentration applies to thereaction medium at the start of the extraction and in a continuousprocess applies to the starting point in the extraction. Theconcentration of (meth)acrylic acid at the end of the extraction willdepend on the number of stages but will preferably be below 50%, morepreferably 30%, most preferably 20% of the starting level.

Advantageously, concentrations of the (meth)acrylic acid at these levelsresult in better extraction into the organic phase.

Generally, the base catalyst molar concentration in the aqueous reactionmedium during the extraction of (meth)acrylic acid therefrom is≦theoverall acid concentration therein mol/mol, more preferably, the basecatalyst molar concentration ≦75% mol/mol of the overall acidconcentration during the extraction, most preferably, the base catalystmolar concentration in the aqueous reaction medium during the extractionof (meth)acrylic acid therefrom is≦the non (meth)acrylic acid acidconcentration mol/mol, more especially, ≦80% of the non (meth)acrylicacid acid concentration mol/mol during the extraction.

Preferably, the molar level of base catalyst to the said at least onedicarboxylic acid and/or pre-cursor thereof is maintained at asub-stoichiometric level in relation to the formation of the first acidsalt thereof during the extraction process and the amount ofdicarboxylic acid added is determined accordingly.

Suitable mixtures of dicarboxylic acid for the production of methacrylicacid are itaconic, citramalic, citraconic and mesaconic acid, morepreferably, itaconic, citramalic and citraconic acid. Suitable mixturesof dicarboxylic acid for the production of acrylic acid are maleic,fumaric, and malic acid, more preferably, malic acid.

Advantageously, the extraction does not require addition of any processexternal agents to the aqueous phase so that the aqueous phase caneasily and efficiently be recycled into the decarboxylation reactionmedium for further decarboxylation under base catalysed conditionsfollowed by further extraction. In this way no or little additional baseis required to process further dicarboxylic acid to (meth)acrylic acid.Equally the only acids added to the system are those dicarboxylic acidsand/or pre-cursor acids involved in the production of (meth)acrylic acidor those acids formed in the production process. No external inorganicacid is required.

According to a second aspect of the present invention there is provideda method of extracting (meth)acrylic acid from an aqueous reactionmedium, the aqueous reaction medium being formed from at least one basecatalyst and at least one dicarboxylic acid selected from fumaric,maleic, malic, itaconic, citraconic, mesaconic or citramalic acid ormixtures thereof in aqueous solution and containing the base catalyseddecarboxylation products thereof including (meth)acrylic acid or(meth)acrylate base salt, the method comprising the steps of introducingan organic solvent to the aqueous reaction medium for solvent extractionof the (meth)acrylic acid into the organic phase characterised in thatthe level of base catalyst to the said at least one dicarboxylic acidand/or pre-cursor thereof is maintained at a sub-stoichiometric level inrelation to the formation of the first acid salt thereof during theextraction process.

According to a further aspect of the present invention there is provideda method of extracting (meth)acrylic acid from an aqueous reactionmedium into an organic phase in contact therewith, the aqueous reactionmedium being formed from at least one base catalyst and at least onedicarboxylic acid selected from fumaric, maleic, malic, itaconic,citraconic, mesaconic or citramalic acid or mixtures thereof in aqueoussolution and containing the base catalysed decarboxylation productsthereof including (meth)acrylic acid or (meth)acrylate base salt and theorganic phase comprises a suitable organic solvent for the said(meth)acrylic acid characterised in that in the aqueous reaction mediumthe relative level of base catalyst to the said at least onedicarboxylic acid and/or pre-cursor thereof is maintained at asub-stoichiometric level in relation to the formation of the first acidsalt thereof during at least part of the extraction.

According to a still further aspect of the present invention there isprovided a method of extracting (meth)acrylic acid from an aqueousreaction medium, the aqueous reaction medium being formed from at leastone base catalyst and at least one dicarboxylic acid selected frommaleic, fumaric, malic, itaconic, citraconic, mesaconic or citramalicacid or mixtures thereof in aqueous solution and containing the basecatalysed decarboxylation products thereof including (meth)acrylic acidand/or (meth)acrylate base salt, the method comprising the step ofsolvent extraction of the (meth)acrylic acid into an organic phasecomprising an organic solvent in contact with the said aqueous reactionmedium wherein the method is characterised in that there is added anadditional amount of at least one of the said dicarboxylic acids and/ora pre-cursor thereof to the said aqueous reaction medium containing thesaid base catalysed decarboxylation products thereof to enhance thesolvent extraction of the (meth)acrylic acid into the organic phase.

Preferably, the method of any aspect herein includes the step ofseparating the organic phase from the aqueous phase after extractionfollowed by subsequent treatment of the organic phase to isolate the(meth)acrylic acid extracted in the extraction process from the organicsolvent. A suitable treatment of the organic phase is distillation toobtain the (meth)acrylic acid.

It will be understood that the dicarboxylic acid being a dibasic acidcan form a first and second acid salt thereof with a base and the termfirst acid salt should be understood accordingly and is not intended torefer to the salt with a second or further acid group on thedicarboxylic acid or pre-cursor thereof but only the first acid saltthat forms.

Advantageously, by maintaining the base at sub-stoichiometric first acidsalt levels with respect to the level of dicarboxylic acid and/orpre-cursor in the aqueous medium/reaction medium the extraction of the(meth)acrylic acid into the suitable organic solvent is improved.

Preferably, in the case of decomposition of acids for the formation ofMAA, the organic solvent is an external organic solvent with respect tothe aqueous medium/reaction medium.

Preferably, at least some citraconic acid is present in the aqueousmedium. Advantageously, this improves the extraction. However, the mostsuitable acid currently is itaconic acid due to its commercialavailability or citramalic acid.

A suitable pre-cursor is one which can be re-cycled to produce one ormore of the said dicarboxylic acids. Typically, the pre-cursor willdecompose under suitable conditions of temperature and pressure toproduce the said dicarboxylic acids. Accordingly, the pre-cursor may beregarded as a source of the dicarboxylic acid. It will be appreciatedthat a base catalyst is already present so that the pre-cursordecomposition may advantageously be base catalysed under such suitableconditions. A suitable pre-cursor for the itaconic, citraconic,mesaconic or citramalic acids is citric acid which may be dehydrated anddecarboxylated to produce at least one of itaconic, citraconic,mesaconic acids or decarboxylated to produce citramalic acid. Thisreaction takes place under suitable conditions of temperature andpressure and optionally in the presence of the base catalyst without thenecessity of a further separate catalyst. However, it has been foundthat adding citric acid to the aqueous medium/reaction medium prior toextraction also assists the extraction of the methacrylic acid as theadded acid whilst also not introducing an external reagent which itselfneeds to be removed from the aqueous medium/reaction medium because thecitric acid can then be treated subsequently to generate moredicarboxylic acid and thence methacrylic acid in a continuous process.

According to a third aspect of the present invention there is provided aprocess for the production of (meth)acrylic acid comprising the stepsof:—

forming an aqueous medium of at least one base catalyst and at least onedicarboxylic acid selected from fumaric, maleic, malic, itaconic,citraconic, mesaconic or citramalic acid or mixtures thereof;

decarboxylating the at least one dicarboxylic acid in the presence ofthe at least one base catalyst under suitable conditions of temperatureand pressure to produce (meth)acrylic acid and/or base salts thereof inthe aqueous medium;

introducing an organic solvent to the said aqueous medium for solventextraction of the (meth)acrylic acid into an organic phase;

characterised in that the level of base catalyst to the said at leastone dicarboxylic acid and/or pre-cursor thereof is maintained at asub-stoichiometric level in relation to the formation of the first acidsalt thereof during the extraction process.

In any aspect herein, the organic solvent may be introduced to theaqueous medium before or after decarboxylation.

Preferably, the sub-stoichiometric level is maintained, after, ifnecessary, being implemented post reaction by added acid, during atleast that part of the extraction process herein which is carried outafter the decarboxylation step.

According to a fourth aspect of the present invention there is provideda process for the production of (meth)acrylic acid comprising the stepsof:—

forming an aqueous medium of at least one base catalyst and at least onedicarboxylic acid selected from fumaric, maleic, malic, itaconic,citraconic, mesaconic or citramalic acid or mixtures thereof;

decarboxylating the at least one dicarboxylic acid in the presence ofthe at least one base catalyst under suitable conditions of temperatureand pressure to produce (meth)acrylic acid and/or base salts thereof inthe aqueous medium;

introducing an organic solvent to the said aqueous medium for solventextraction of the (meth)acrylic acid into an organic phase;

characterised by the step of adding an additional amount of at least oneof the said dicarboxylic acids and/or a pre-cursor thereof to the saidaqueous medium, preferably, after the decarboxylation step to enhancethe solvent extraction of the (meth)acrylic acid into the organic phase.

Advantageously, in accordance with some embodiments of the invention, itis also possible to maintain the level of base catalyst to the said atleast one dicarboxylic acid and/or pre-cursor thereof at asub-stoichiometric level in relation to the formation of the first acidsalt thereof during the decarboxylation.

Suitable organic solvents for (meth)acrylic acid extraction includehydrocarbon solvents or oxygenated solvents, particularly C₄-C₂₀hydrocarbon solvents. The hydrocarbon solvents may be aliphatic,aromatic, or part aromatic, saturated or unsaturated, cyclic, acyclic orpart cyclic, linear or branched. The oxygenated solvents may be esters,ethers or ketones. Suitable solvents include toluene, benzene,ethylbenzene, xylene, trimethylbenzene, octane, heptane, hexane,pentane, cyclopentane, cyclohexane, cycloheptane, cyclooctane,cyclohexene, methylcyclohexane, methylethylketone, methyl methacrylateor mixtures thereof. Ionic liquids which are immiscible with water mayalso be used.

A preferred mixture of solvents for the extraction of MAA is a C₄-C₂₀hydrocarbon solvent and MMA. A suitable mixture contains 1-40% MMA, moretypically, 5-30% MMA with the balance made up of the hydrocarbonsolvent(s). Preferred hydrocarbon solvents for this purpose are tolueneand xylenes.

Nevertheless, it is preferred to use only C₄-C₂₀ hydrocarbons eitheralone or in mixtures with other hydrocarbons as the extractive solvent.Preferably, the relative (static) permittivity of the hydrocarbon oreach of the hydrocarbons in a mixture of hydrocarbons is less than 20,more preferably, less than 8, most preferably, less than 3 at 20° C. andatmospheric pressure. Accordingly, hydrocarbons having relative (static)permittivity in the range 1.6 to 20 are preferred, more preferably inthe range 1.7 to 8, most preferably, in the range 1.8 to 3 at 20° C. andatmospheric pressure.

The preferred solvents and mixtures for extraction of AA have relative(static) permittivity of less than 20, more preferably, less than 10,most preferably, less than 7 at 20° C. and atmospheric pressure.Typically, the relative (static) permittivity is at least 1.6, moretypically, at least, 2.0, most typically, at least, 2.3. Accordingly,solvents having relative (static) permittivity in the range 1.6 to 20are preferred, more preferably in the range 2.0 to 10, most preferably,in the range 2.2 to 8 all at 20° C. and atmospheric pressure.

The dicarboxylic acid(s) reactants and the base catalyst need notnecessarily be the only compounds present in the aqueous medium/reactionmedium. The dicarboxylic acid(s) together with any other compoundspresent are generally dissolved in an aqueous solution for the basecatalysed thermal decarboxylation.

Preferably, the base catalysed decarboxylation of the at least onedicarboxylic acid takes place at less than 350° C., typically, less than330° C., more preferably, at up to 310° C., most preferably at up to300° C. In any case, a preferred lower temperature for thedecarboxylation process of the present invention is 200° C. Preferredtemperature ranges for the decarboxylation process of the presentinvention are between 200 and up to 349° C., more preferably, between220 and 320° C., most preferably, between 240 and 310° C., especiallybetween 240 and 290° C. An especially preferred temperature range is240-275° C., most especially, 245-275° C.

The base catalysed decarboxylation reaction takes place at a temperatureat which the aqueous medium/reaction medium is in the liquid phase.Typically, the aqueous medium/reaction medium is an aqueous solution.

Preferably, the base catalysed decarboxylation takes place with thedicarboxylic acid reactants and preferably the base catalyst in aqueoussolution.

Advantageously, carrying out the decarboxylation at lower temperaturesprevents the production of significant amounts of by-products which maybe difficult to remove and may cause further purification and processingproblems in an industrial process. Therefore, the process provides asurprisingly improved selectivity in this temperature range.Furthermore, lower temperature decarboxylation uses less energy andthereby creates a smaller carbon footprint than high temperaturedecarboxylations.

Preferably, the extraction step of the (meth)acrylic acid takes place atless than or equal to the decarboxylation temperatures detailed above,more preferably however at less than 100° C., most preferably, at lessthan 80° C., especially less than 60° C. In any case, a preferred lowertemperature for the extraction step of the present invention is −10° C.,more preferably, 0° C. Preferred temperature ranges for the extractionstep of the present invention are between −10 and up to 349° C., morepreferably, between −10 and 100° C., most preferably, between 0 and 80°C., especially between 10 and 60° C., more especially 30-50° C.

The extraction step takes place at a temperature at which the organicand aqueous phases are in the liquid phase.

Accordingly, the extraction step takes place at a pressure at which theorganic and aqueous phases are in the liquid phase, generally,extraction takes place at atmospheric pressure.

The dicarboxylic acids are available from non-fossil fuel sources. Forinstance, the itaconic, citramalic, citraconic or mesaconic acids couldbe produced from pre-cursors such as citric acid or isocitric acid bydehydration and decarboxylation at suitably high temperatures or fromaconitic acid by decarboxylation at suitably high temperatures. It willbe appreciated that a base catalyst is already present so that thepre-cursor may be subjected to base catalysed dehydration and/ordecomposition. Citric acid and isocitric acid may themselves be producedfrom known fermentation processes and aconitic acid may be produced fromthe former acids. Accordingly, the process of the invention goes someway to providing a biological or substantially biological route togenerate (meth)acrylates directly whilst minimising reliance on fossilfuels.

U.S. Pat. No. 5,849,301 discloses a process for production of malic andfumaric acids from glucose. U.S. Pat. No. 5,766,439 discloses a processfor production of maleic acid. Malic acid is also available byextraction of products produced in agriculture such as apple juice.

To maintain the reactants in the liquid phase under the abovetemperature conditions the decarboxylation reaction of the at least onedicarboxylic acid is carried out at suitable pressures in excess ofatmospheric pressure. Suitable pressures which will maintain thereactants in the liquid phase in the above temperature ranges aregreater than 200 psi, more suitably, greater than 300 psi, mostsuitably, greater than 450 psi and in any case at a higher pressure thanthat below which the reactant medium will boil. There is no upper limitof pressure but the skilled person will operate within practical limitsand within apparatus tolerances, for instance, at less than 10,000 psi,more typically, at less than 5,000 psi, most typically, at less than4000 psi.

Preferably, the above decarboxylation reaction is at a pressure ofbetween about 200 and 10000 psi. More preferably, the reaction is at apressure of between about 300 and 5000 psi and yet more preferablybetween about 450 and 3000 psi.

In a preferred embodiment, the above reaction is at a pressure at whichthe aqueous medium/reaction medium is in the liquid phase.

The above reaction is at a temperature and pressure at which the aqueousmedium/reaction medium is in the liquid phase.

As mentioned above, the catalyst is a base catalyst.

Preferably, the catalyst comprises a source of OH⁻ ions. Preferably, thebase catalyst comprises a metal oxide, hydroxide, carbonate, acetate(ethanoate), alkoxide, hydrogencarbonate or salt of a decomposable di-or tri-carboxylic acid, or a quaternary ammonium compound of one of theabove; more preferably a Group I or Group II metal oxide, hydroxide,carbonate, acetate, alkoxide, hydrogencarbonate or salt of a di- ortri-carboxylic acid or (meth)acrylic acid. The base catalyst may alsocomprise one or more amines.

Preferably, the base catalyst is selected from one or more of thefollowing: LiOH, NaOH, KOH, Mg(OH)₂, Ca(OH)₂, Ba(OH)₂, CsOH, Sr(OH)₂,RbOH, NH₄OH, Li₂CO₃, Na₂CO₃, K₂CO₃, Rb₂CO₃, Cs₂CO₃, MgCO₃, CaCO₃, SrCO₃,BaCO₃, (NH₄)₂CO₃, LiHCO₃, NaHCO₃, KHCO₃, RbHCO₃, CsHCO₃, Mg(HCO₃)₂,Ca(HCO₃)₂, Sr(HCO₃)₂, Ba(HCO₃)₂, NH₄HCO₃, Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O,MgO, CaO, SrO, BaO, Li(OR¹), Na(OR¹), K(OR¹), Rb(OR¹), Cs(OR¹),Mg(OR¹)₂, Ca(OR¹)₂, Sr(OR¹)₂, Ba(OR¹)₂, NH₄(OR¹) where R¹ is any C₁ toC₆ branched, unbranched or cyclic alkyl group, being optionallysubstituted with one or more functional groups; NH₄(RCO₂), Li(RCO₂),Na(RCO₂), K(RCO₂), Rb(RCO₂), Cs(RCO₂), Mg(RCO₂)₂, Ca(RCO₂)₂, Sr(RCO₂)₂or Ba(RCO₂)₂, where RCO₂ is selected from malate, fumarate, maleate,citramalate, mesaconate, citraconate, itaconate, citrate, oxalate and(meth)acrylate; (NH₄)₂(CO₂RCO₂), Li₂(CO₂RCO₂), Na₂CO₂RCO₂), K₂(CO₂RCO₂)Rb₂(CO₂RCO₂) Cs₂(CO₂RCO₂), Mg(CO₂RCO₂), Ca(CO₂RCO₂) Sr(CO₂RCO₂),Ba(CO₂RCO₂), (NH₄)₂(CO₂RCO₂), where CO₂RCO₂ is selected from malate,fumarate, maleate, citramalate, mesaconate, citraconate, itaconate andoxalate; (NH₄)₃(CO₂R(CO₂)CO₂) Li₃(CO₂R(CO₂)CO₂), Na₃(CO₂R(CO₂)CO₂) K₃(CO₂R(CO₂)CO₂), Rb₃(CO₂R(CO₂)CO₂), Cs₃(CO₂R(CO₂)CO₂), Mg₃(CO₂R(CO₂)CO₂)₂Ca₃(CO₂R(CO₂)CO₂)₂, Sr₃ (CO₂R(CO₂)CO₂) Ba₃(CO₂R(CO₂)CO₂)₂, (NH₄)₃(CO₂R(CO₂)CO₂), where CO₂R(CO₂)CO₂ is selectedfrom citrate, isocitrate and aconitate; methylamine, ethylamine,propylamine, butylamine, pentylamine, hexylamine, cyclohexylamine,aniline; and R₄NOH where R is selected from methyl, ethyl propyl, butyl.More preferably, the base is selected from one or more of the following:LiOH, NaOH, KOH, Mg(OH)₂, Ca(OH)₂, Ba(OH)₂, CsOH, Sr(OH)₂, RbOH, NH₄OH,Li₂CO₃, Na₂CO₃, K₂CO₃, Rb₂CO₃, Cs₂CO₃, MgCO₃CaCO₃, (NH₄)₂CO₃, LiHCO₃,NaHCO₃, KHCO₃RbHCO₃, CsHCO₃, Mg(HCO₃)₂, Ca(HCO₃)₂Sr(HCO₃)₂Ba(HCO₃)₂,NH₄HCO₃, Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O; NH₄(RCO₂), Li(RCO₂), Na(RCO₂),K(RCO₂), Rb(RCO₂), Cs(RCO₂), Mg(RCO₂)₂, Ca(RCO₂)₂, Sr(RCO₂)₂ orBa(RCO₂)₂, where RCO₂ is selected from malate, fumarate, maleate,itaconate, citrate, oxalate, (meth)acrylate; (NH₄)₂(CO₂RCO₂)Li₂(CO₂RCO₂) Na₂(CO₂RCO₂) K₂(CO₂RCO₂) Rb₂(CO₂RCO₂) Cs₂(CO₂RCO₂)Mg(CO₂RCO₂) Ca(CO₂RCO₂), Sr(CO₂RCO₂), Ba(CO₂RCO₂), (NH₄)₂(CO₂RCO₂),where CO₂RCO₂ is selected from malate, fumarate, maleate, citramalate,mesaconate, citraconate, itaconate, oxalate; (NH₄)₃(CO₂R(CO₂)CO₂),Li₃(CO₂R(CO₂)CO₂), Na₃(CO₂R(CO₂)CO₂), K₃(CO₂R(CO₂)CO₂),Rb₃(CO₂R(CO₂)CO₂), Cs₃(CO₂R(CO₂)CO₂), Mg₃(CO₂R(CO₂)CO₂)₂,Ca₃(CO₂R(CO₂)CO₂)₂, Sr₃(CO₂R(CO₂)CO₂)₂, Ba₃(CO₂R(CO₂)CO₂)₂,(NH₄)₃(CO₂R(CO₂)CO₂), where CO₂R(CO₂)CO₂ is selected from citrate,isocitrate; tetramethylammonium hydroxide and tetraethylammoniumhydroxide. Most preferably, the base is selected from one or more of thefollowing: NaOH, KOH, Ca(OH)₂, CsOH, RbOH, NH₄OH, Na₂CO₃, K₂CO₃, Rb₂CO₃,Cs₂CO₃, MgCO₃, CaCO₃, (NH₄)₂CO₃, NH₄ (RCO₂), Na(RCO₂), K(RCO₂),Rb(RCO₂), Cs(RCO₂), Mg(RCO₂)₂, Ca(RCO₂)₂, Sr(RCO₂)₂ or Ba(RCO₂)₂, whereRCO₂ is selected from malate, fumarate, maleate, itaconate, citrate,oxalate, (meth)acrylate; (NH₄)₂(CO₂RCO₂) Na₂(CO₂RCO₂) K₂(CO₂RCO₂)Rb₂(CO₂RCO₂) Cs₂(CO₂RCO₂) Mg(CO₂RCO₂) Ca(CO₂RCO₂) (NH₄)₂(CO₂RCO₂), whereCO₂RCO₂ is selected from malate, fumarate, maleate, citramalate,mesaconate, citraconate, itaconate, oxalate; (NH₄)₃(CO₂R(CO₂)CO₂) Na₃(CO₂R(CO₂)CO₂), K₃ (CO₂R(CO₂)CO₂), Rb₃ (CO₂R(CO₂)CO₂), Cs₃(CO₂R(CO₂)CO₂) Mg₃ (CO₂R(CO₂)CO₂)₂, Ca₃ (CO₂R(CO₂)CO₂)₂,(NH₄)₃(CO₂R(CO₂)CO₂), where CO₂R(CO₂)CO₂ is selected from citrate,isocitrate; and tetramethylammonium hydroxide.

The catalyst may be homogeneous or heterogeneous. In one embodiment, thecatalyst may be dissolved in a liquid reaction phase. However, thecatalyst may be suspended on a solid support over which the reactionphase may pass. In this scenario, the reaction phase is preferablymaintained in a liquid, more preferably, an aqueous phase.

Preferably, the effective mole ratio of base OH⁻:acid for thedecarboxylation reaction is between 0.001-2:1, more preferably,0.01-1.2:1, most preferably, 0.1-1:1, especially, 0.3-1:1. By theeffective mole ratio of base OH⁻ is meant the nominal molar content ofOH⁻ derived from the compounds concerned.

By acid is meant the moles of acid. Thus, in the case of a monobasicbase, the effective mole ratios of base OH⁻:acid will coincide withthose of the compounds concerned but in the case of di or tribasic basesthe effective mole ratio will not coincide with that of mole ratio ofthe compounds concerned.

Specifically, this may be regarded as the mole ratio of monobasic base:di or tri carboxylic acid is preferably between 0.001-2:1, morepreferably, 0.01-1.2:1, most preferably, 0.1-1:1, especially, 0.3-1:1.

As the deprotonation of the acid to form the salt is only referring to afirst acid deprotonation in the present invention, in the case of di ortribasic bases, the mole ratio of base above will vary accordingly.

Optionally, the (meth)acrylic acid product may be esterified to producean ester thereof. Potential esters may be selected from C₁-C₁₂ alkyl orC₂-C₁₂ hydroxyalkyl, glycidyl, isobornyl, dimethylaminoethyl,tripropyleneglycol esters. Most preferably the alcohols or alkenes usedfor forming the esters may be derived from bio sources, e.g.biomethanol, bioethanol, biobutanol.

As mentioned above, the pre-cursor such as citric acid, isocitric acidor aconitic acid preferably decomposes under suitable conditions oftemperature and pressure and optionally in the presence of base catalystto one of the dicarboxylic acids of the invention. Suitable conditionsfor this decomposition are less than 350° C., typically, less than 330°C., more preferably, at up to 310° C., most preferably at up to 300° C.In any case, a preferred lower temperature for the decomposition is 180°C. Preferred temperature ranges for the pre-cursor decomposition arebetween 190 and up to 349° C., more preferably, between 200 and 300° C.,most preferably, between 220 and 280° C., especially between 220 and260° C.

The pre-cursor decomposition reaction takes place at a temperature atwhich the aqueous reaction medium is in the liquid phase.

To maintain the reactants in the liquid phase under the above pre-cursordecomposition temperature conditions the decarboxylation reaction iscarried out at suitable pressures in excess of atmospheric pressure.Suitable pressures which will maintain the reactants in the liquid phasein the above temperature ranges are greater than 150 psi, more suitably,greater than 180 psi, most suitably, greater than 230 psi and in anycase at a higher pressure than that below which the reactant medium willboil. There is no upper limit of pressure but the skilled person willoperate within practical limits and within apparatus tolerances, forinstance, at less than 10,000 psi, more typically, at less than 5,000psi, most typically, at less than 4000 psi.

Preferably, the pre-cursor decomposition reaction is at a pressure ofbetween about 150 and 10000 psi. More preferably, the reaction is at apressure of between about 180 and 5000 psi and yet more preferablybetween about 230 and 3000 psi.

In a preferred embodiment, the pre-cursor decomposition reaction is at apressure at which the reaction medium is in the liquid phase.

Preferably, the pre-cursor decomposition reaction is at a temperatureand pressure at which the aqueous reaction medium is in the liquidphase.

According to a further aspect of the present invention there is provideda method of preparing polymers or copolymers of (meth)acrylic acid or(meth)acrylic acid esters, comprising the steps of

(i) preparation of (meth)acrylic acid in accordance with the third orfourth aspect of the present invention;

(ii) optional esterification of the (meth)acrylic acid prepared in (i)to produce the (meth)acrylic acid ester;

(iii) polymerisation of the (meth)acrylic acid prepared in (i) and/orthe ester prepared in (ii), optionally with one or more comonomers, toproduce polymers or copolymers thereof.

Preferably, the (meth)acrylic acid ester of (ii) above is selected fromC₁-C₁₂ alkyl or C₂-C₁₂ hydroxyalkyl, glycidyl, isobornyl,dimethylaminoethyl, tripropyleneglycol esters, more preferably, ethyl,n-butyl, i-butyl, hydroxymethyl, hydroxypropyl or methyl methacrylate,most preferably, methyl methacrylate, ethyl acrylate, butyl methacrylateor butyl acrylate.

Advantageously, such polymers will have an appreciable portion if notall of the monomer residues derived from a source other than fossilfuels.

In any case, preferred comonomers include for example, monoethylenicallyunsaturated carboxylic acids and dicarboxylic acids and theirderivatives, such as esters, amides and anhydrides.

Particularly preferred comonomers are acrylic acid, methyl acrylate,ethyl acrylate, propyl acrylate, n-butyl acrylate, iso-butyl acrylate,t-butyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate,iso-bornyl acrylate, methacrylic acid, methyl methacrylate, ethylmethacrylate, propyl methacrylate, n-butyl methacrylate, iso-butylmethacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate,hydroxyethyl methacrylate, lauryl methacrylate, glycidyl methacrylate,hydroxypropyl methacrylate, iso-bornyl methacrylate, dimethylaminoethylmethacrylate, tripropyleneglycol diacrylate, styrene, α-methyl styrene,vinyl acetate, isocyanates including toluene diisocyanate andp,p′-methylene diphenyl diisocyanate, acrylonitrile, butadiene,butadiene and styrene (MBS) and ABS subject to any of the abovecomonomers not being the momomer selected from methacrylic acid or amethacrylic acid ester in (i) or (ii) above in any givencopolymerisation of the said acid monomer in (i) or a said ester monomerin (ii) with one or more of the comonomers.

It is of course also possible to use mixtures of different comonomers.The comonomers themselves may or may not be prepared by the same processas the monomers from (i) or (ii) above.

According to a further aspect of the present invention there is providedpolyacrylic acid, polymethacrylic acid, polyalkylacrylate,polymethylmethacrylate (PMMA) and polybutylmethacrylate homopolymers orcopolymers formed from the method of preparing polymers or copolymers ofthe above aspect.

According to a still further aspect of the present invention there isprovided a process for the production of methacrylic acid comprising:—

providing a source of a pre-cursor acid selected from aconitic, citricand/or isocitric acid;

performing a decarboxylation and, if necessary, a dehydration step onthe source of pre-cursor acid by exposing the source thereof in thepresence or absence of base catalyst to a sufficiently high temperatureto provide itaconic, mesaconic, citraconic and/or citramalic acid; anduse of the itaconic, mesaconic, citraconic and/or citramalic acidprovided in a process according to any of the other aspects of thepresent invention to provide methacrylic acid and/or enhance extractionthereof into an organic phase.

By a source of aconitic, citric and/or isocitric acid is meant the acidsand salts thereof such as group I or II metal salts thereof and includessolutions of the pre-cursor acids and salts thereof, such as aqueoussolutions thereof.

Optionally, the salt may be acidified to liberate the free acid priorto, during or after the pre-cursor acid decarboxylation step.

Preferably, the dicarboxylic acid(s) reactant(s) or the pre-cursorsthereof of the present invention are exposed to the reaction conditionsfor a suitable time period to effect the required reaction, typically,for a time period of at least 30 seconds, more preferably at least about100 seconds, yet more preferably at least about 120 seconds and mostpreferably at least about 150 seconds.

Typically, the dicarboxylic acid(s) reactant(s) or pre-cursors thereofare exposed to the reaction conditions for a time period of less thanabout 2000 seconds, more typically less than about 1500 seconds, yetmore typically less than about 1000 seconds.

Preferably, the dicarboxylic acid(s) reactant(s) or the pre-cursorsthereof of the present invention are exposed to the reaction conditionsfor a time period of between about 75 seconds and 2500 seconds, morepreferably between about 90 seconds and 1800 seconds and most preferablybetween about 120 seconds and 800 seconds.

Preferably, the dicarboxylic acid(s) reactant(s) or the pre-cursorsthereof of the present invention are dissolved in water so that thereaction occurs under aqueous conditions.

It will be clear from the way in which the above reactions are definedthat if the pre-cursor is decarboxylated and, if necessary, dehydratedin a reaction medium then the reaction medium may simultaneously beeffecting base catalysed decarboxylation of the at least onedicarboxylic acid selected from maleic, fumaric, malic, itaconic,citraconic, mesaconic, citramalic acid or mixtures thereof produced fromthe pre-cursor thereof according to any aspect of the invention.Accordingly, the decarboxylation and if necessary, dehydration of thepre-cursor and the base catalysed decarboxylation of the at least onedicarboxylic acid may take place in one reaction medium i.e. the twoprocesses may take place as a one pot process. However, it is preferredif the pre-cursor is decarboxylated and, if necessary, dehydratedsubstantially without base catalysis so that the decarboxylation and ifnecessary, dehydration of the pre-cursor and the base catalyseddecarboxylation of the at least one dicarboxylic acid take place inseparate steps.

Preferably, the concentration of the dicarboxylic acid reactant(s) inthe decarboxylation reaction is at least 0.1M, preferably in an aqueoussource thereof; more preferably at least about 0.2M, preferably in anaqueous source thereof; most preferably at least about 0.3M, preferablyin an aqueous source thereof, especially, at least about 0.5M.Generally, the aqueous source is an aqueous solution.

Preferably, the concentration of the dicarboxylic acid reactant(s) inthe decarboxylation reaction is less than about 10M, more preferably,less than 8M, preferably in an aqueous source thereof; more preferably,less than about 5M, preferably in an aqueous source thereof; morepreferably less than about 3M, preferably in an aqueous source thereof.

Preferably, the concentration of the dicarboxylic acid reactant(s) inthe decarboxylation reaction is in the range 0.05M-20, typically,0.05-10M, more preferably, 0.1M-5M, most preferably, 0.3M-3M.

The base catalyst may be dissolvable in a liquid medium, which may bewater or the base catalyst may be heterogeneous. The base catalyst maybe dissolvable in the aqueous medium/reaction medium so that reaction iseffected by exposing the reactants to a temperature in excess of that atwhich base catalysed decarboxylation of the reactant(s) to (meth)acrylicacid and/or the pre-cursor acids to the dicarboxylic acids will occursuch as those temperatures given above. The catalyst may be in anaqueous solution. Accordingly, the catalyst may be homogenous orheterogeneous but is typically homogenous. Preferably, the concentrationof the catalyst in the aqueous medium/reaction medium (including thedecomposition of pre-cursor acid medium) is at least 0.1M or greater,preferably in an aqueous source thereof; more preferably at least about0.2M, preferably in an aqueous source thereof; more preferably at leastabout 0.3M.

Preferably, the concentration of the catalyst in the aqueousmedium/reaction medium (including the decomposition of pre-cursor acidmedium) is less than about 10M, more preferably, less than about 5M,more preferably less than about 2M and, in any case, preferably lessthan or equal to that which would amount to a saturated solution at thetemperature and pressure of the reaction.

Preferably, the mole concentration of OH⁻ in the aqueous medium/reactionmedium or pre-cursor acid decomposition is in the range 0.05M-20M, morepreferably, 0.1-5M, most preferably, 0.2M-2M.

Preferably, the reaction conditions are weakly acidic. Preferably, thereaction pH is between about 2 and 9, more preferably between about 3and about 6.

For the avoidance of doubt, by the term itaconic acid, is meant thefollowing compound of formula (i)

For the avoidance of doubt, by the term citraconic acid, is meant thefollowing compound of formula (ii)

For the avoidance of doubt, by the term mesaconic acid, is meant thefollowing compound of formula (iii)

For the avoidance of doubt, by the term citramalic acid, is meant thefollowing compound of formula (iv)

As mentioned above, the processes of the present invention may behomogenous or heterogeneous. In addition, the process may be a batch orcontinuous process.

Advantageously, one by-product in the production of MAA may be hydroxyisobutyric acid (HIB) which exists in equilibrium with the product MAAat the conditions used for decomposition of the dicarboxylic acids.Accordingly, partial or total separation of the MAA from the products ofthe decomposition reaction shifts the equilibrium from HIB to MAA thusgenerating further MAA during the extraction process or in subsequentprocessing of the solution after separation of MAA. Optionally thesolvent may be present during the decomposition reaction so that aportion at least of the methacrylic acid is extracted into the organicmedium during the decomposition reaction.

Advantageously, one by-product in the production of AA may be hydroxypropionic acid (HPA) which exists in equilibrium with the product AA atthe conditions used for decomposition of the dicarboxylic acids.Accordingly, partial or total separation of the AA from the products ofthe decomposition reaction shifts the equilibrium from HPA to AA thusgenerating further AA during the extraction process or in subsequentprocessing of the solution after separation of AA. Optionally thesolvent may be present during the decomposition reaction so that aportion at least of the acrylic acid is extracted into the organicmedium during the decomposition reaction.

Where a compound of a formula herein may exist as more than onestereoisomer, for example a compound of formula (iv) above, allstereoisomers are included within the scope of the invention. Inparticular, R+ or S− forms of citramalic acid as well as racemicmixtures thereof are included within the scope of the term citramalicacid.

All of the features contained herein may be combined with any of theabove aspects, in any combination.

For a better understanding of the invention, and to show how embodimentsof the same may be carried into effect, reference will now be made, byway of example, to the following figures and examples in which:—

FIG. 1 shows the concentration dependence of the extraction of MAA intotoluene;

FIG. 2 shows a plot of partition coefficient for a range of acidsagainst MMA fraction in toluene;

FIG. 3 shows a plot of relative partition coefficient for a range ofacids with MMA against MMA fraction in toluene;

FIG. 4 shows the effect of adding base and dicarboxylic acid on transferof MAA between aqueous and organic phases;

FIG. 5 shows the distribution of acrylic acid between water and toluene;

FIG. 6 shows a schematic view of suitable apparatus for the basecatalysed decomposition of dicarboxylic acids.

SOLVENT EXTRACTION

The following experimental conditions were used unless indicatedotherwise:—

-   -   0.1M Acids    -   1:1 vol:vol aq:solvent    -   Room Temperature    -   1 minutes agitation time; 5 min settling time    -   Solvent is toluene unless where stated    -   Analysis by HPLC

Comparative Example 1

A series of solvents were tested to examine the extent of transfer ofmethacrylic acid from an aqueous solution using the above procedure. Theresults are shown in table 1.

TABLE 1 Average % relative (static) Solvent Transfer permittivity MixedXylenes 45.3 2.3 Toluene 48.2 2.4 Hexane 27.6 1.9 Benzene 50.1 2.3Pentane 28.3 1.8 Cyclohexane 26.9 2.0 MMA 84.3 6.3

This example shows that MAA present in the free acid form can beefficiently extracted into a range of solvents. Aromatic hydrocarbonsgive the highest extraction efficiencies.

Comparative Example 2

Monobasic and dibasic acids likely to be present in aqueous solutionfollowing partial decomposition of mono and dicarboxylic acids expectedto be found from decomposition of dibasic or tribasic acids werecompared for their solubility in toluene.

Each acid, initially at 0.1M solution in water was separately tested forsolubility in an equal volume of toluene. The results are shown in table2

TABLE 2 Fraction Transferred to Acid Toluene/% monobasic MAA 54.4 CT40.11 HIB 4.21 PY 0 dibasic IC 0 MC 0.64 MAA Methacrylic Acid CTCrotonic Acid HIB Hydroxyisobutyric Acid PY Pyruvic Acid IC ItaconicAcid MC Mesaconic Acid

This example shows that the di and tricarboxylic acids useful in theprocess for the production of MAA are not soluble in toluene, onesolvent which can be employed for the extraction of MAA. Furthermore HIBformed in equilibrium with MAA is not extracted in significantproportions and pyruvic acid formed as an unwanted by-product is alsonot extracted into toluene.

Comparative Example 3

A series of different concentrations of MAA in aqueous solution wereextracted into toluene (1:1 by volume vs aqueous solution). Thepercentage solubility is shown in table 3.

TABLE 3 [MAA] in start- % extracted at 1:1 ing aq soln/M toluene to aqsoln Comp Ex 3a 0.00743 12.69% Comp Ex 3b 0.0148 20.07% Comp Ex 3c0.02878 26.76% Comp Ex 3d 0.05829 37.09% Comp Ex 3e 0.1215 52.00% CompEx 3f 0.2479 60.51% Comp Ex 3g 0.3 63.60% Comp Ex 3h 0.4778 68.67% CompEx 3j 0.7559 73.72% Comp Ex 3k 0.9576 76.71%

The fraction transferred increases with the concentration of MAA. Thedata from table 3 were plotted according to the equation:[MAA]_(tol)=K[MAA]²aqand the value K in the equation was evaluated as 14.6. The results areplotted in FIG. 1.

This example shows that the extraction of MAA into toluene isconcentration dependent. For efficient extraction, concentrations above0.1M are preferred.

Comparative Example 4

Aqueous solutions were prepared of each of the dicarboxylic acidsexemplified in comparative example 2. These were extracted with an equalvolume of solvent mixtures of toluene and methyl methacrylate (MMA). Theresultant degrees of extraction are shown in table 4

TABLE 4 Fraction of MMA in MMA/Toluene solvent mixture IC MC PY MAA HIBCT 0 0 0.64 0 54.4 4.21 40.11 0.1 0 1.72 0 58.85 4.8 46.72 0.2 0.29 4.50.3 63.01 5.14 49.88 0.3 0.81 8.26 0.7 67.25 6.38 53.62 0.4 1.69 13.021.17 70.31 4.82 56.56 0.5 2.89 20.56 2.07 74.28 5.76 61.15 0.6 4.3427.82 3.01 76.77 7.32 64.67 0.7 6.56 38.06 4.17 79.42 19.71 68.07 0.89.57 47.19 5.57 81.42 21.47 70.86 0.9 13.1 56.33 8.05 83.02 23.32 73.211 17.58 63.45 10.71 84.28 23.9 75.05

This example shows that MMA can be added to toluene to improve theextraction efficiency of MAA. However an optimum MMA level is observedabove which dicarboxylic acids and HIB are extracted in significantamounts.

In order to compare the solubilities in the organic solvents in terms ofpartition coefficients each sample was converted to a partitioncoefficient based on the equation:[MAA]_(solv)=K[MAA]² _(aq)

The data are presented in FIG. 2

Only MAA, Crotonic acid and hydroxyisobutyric acid have significantsolubilities in any of the solvent phases. The solubility of thecomponents increases with the fraction of MMA in every case.

The relative partition coefficients may also change with composition.FIG. 3 compares the ratio of Partition Coefficient for MAA with that foreach of the other acids.

Thus the comparative examples show that selectivity is higher if puretoluene is used. However use of some MMA allows a higher concentrationof MAA to be extracted whilst lowering selectivity.

Comparative Example 5

The extraction of a solution of 0.1M MAA in aqueous solution into anequivalent volume of toluene was determined after addition of 0.05Msodium hydroxide. The amount of MAA transferred fell from 48% to 26%.The results are shown in the first two rows of table 5

Examples 1-3

Sufficient itaconic acid to give a 0.1M solution was added to theMAA+sodium hydroxide containing aqueous solution of comparative example5 and the MAA transfer dramatically improved to 44.7% extraction intotoluene. The data are shown in table 5. The experiment was repeated withcitraconic or mesaconic acids instead of Itaconic acid. Very similarresults were obtained.

TABLE 5 Concentration % of MAA in Transfer aqueous Added into solution/MNaOH/M Added Acid/M Toluene Comp Ex 1 0.1 48.0 Comp Ex 5 0.1 0.05 26.0Ex 1 0.1 0.05 Itaconic Acid, 0.1 44.7 Ex 2 0.1 0.05 Citraconic Acid, 0.148.1 Ex 3 0.1 0.05 Mesaconic Acid, 0.1 46.3

Examples 4-30 and Comparative Examples 6-9

0.1M concentrations of various di and tricarboxylic acids added to anaqueous solution of 0.1M MAA containing different levels of NaOH wereextracted with an equal volume of toluene.

The quantity of MAA extracted fell much more slowly as sodium hydroxideconcentration increased, in the presence of one of the added carboxylicacids than in the absence of added di/tri carboxylic acid. The effectwas most marked with citric and mesaconic acids. Table 6 shows theexperimental data, which are presented graphically in FIG. 4.

TABLE 6 [MAA]/M [NaOH]/M Acid [Acid] % transfer Comp Ex 1 0.1 0 None 48Comp Ex 5 0.1 0.05 None 26.04 Comp Ex 6 0.1 0 Itaconic 0.1 47.99 Ex 40.1 0.025 Itaconic 0.1 44.59 Ex 5 0.1 0.05 Itaconic 0.1 41.53 Ex 6 0.10.075 Itaconic 0.1 30.7 Ex 7 0.1 0.1 Itaconic 0.1 20.88 Ex 8 0.1 0.125Itaconic 0.1 17.68 Ex 9 0.1 0.15 Itaconic 0.1 3.84 Comp ex 7 0.1 0Citraconic 0.1 47.58 Ex 10 0.1 0.025 Citraconic 0.1 47.71 Ex 11 0.1 0.05Citraconic 0.1 48.06 Ex 12 0.1 0.075 Citraconic 0.1 47.29 Ex 13 0.1 0.1Citraconic 0.1 45.52 Ex 14 0.1 0.125 Citraconic 0.1 35.05 Ex 15 0.1 0.15Citraconic 0.1 24.21 Ex 16 0.1 0.2 Citraconic 0.1 8.12 Comp Ex 8 0.1 0Mesaconic 0.1 47.36 Ex 17 0.1 0.025 Mesaconic 0.1 46.98 Ex 18 0.1 0.05Mesaconic 0.1 46.32 Ex 19 0.1 0.075 Mesaconic 0.1 45.66 Ex 20 0.1 0.1Mesaconic 0.1 44.05 Ex 21 0.1 0.125 Mesaconic 0.1 39.16 Ex 22 0.1 0.15Mesaconic 0.1 35.15 Ex 23 0.1 0.2 Mesaconic 0.1 23 Comp Ex 9 0.1 0Citric 0.1 47.82 Ex 24 0.1 0.025 Citric 0.1 48.27 Ex 25 0.1 0.05 Citric0.1 48.12 Ex 26 0.1 0.075 Citric 0.1 47.44 Ex 27 0.1 0.1 Citric 0.146.18 Ex 28 0.1 0.125 Citric 0.1 41.83 Ex 29 0.1 0.15 Citric 0.1 39.19Ex 30 0.1 0.2 Citric 0.1 28.35

Examples 31-34

Table 7 illustrates the use of higher organic phase to aqueous phaseratios leading to higher degrees of extraction of a solution of 0.3MMAA.

TABLE 7 aq:toluene v/v % transfer Ex 31 1:1 64 Ex 32 1:2 72 Ex 33 1:3 76Ex 34 1:4 85

Examples 35-39

Table 8 further shows that the use of serial extractions can increasethe MAA transfer still further. The starting solution was 0.3M MAA inwater.

TABLE 8 aq:toluene v/v % transfer 1:1 vol Ex 31 1:1 63.6 1:2 vol Ex 321:2 72.0 Ex 35 2 × 1:1 80.2 1:3 vol Ex 33 1:3 75.9 Ex 36 1:2 + 1:1 84.9Ex 37 3 × 1:1 88.1 1:4 vol Ex 34 1:4 84.9 Ex 38 2 × 1:2 88.0 Ex 39 4 ×1:1 92.4

Example 40

In a further experiment 0.01M citramalic acid decomposition wasconducted with reaction flow in order to test the use of tolueneextraction during the reaction; in this experiment, the flow of aqueoussolution of dicarboxylic acid was mixed with an equal rate of flow oftoluene before entering the reactor. Conditions were as follows: 0.01MCitramalic acid (CM) in water with 50 mM NaOH, 2000 psi at variabletemperature, with a fixed residence time of 480 seconds. Initial flowconsisted of CM and NaOH dissolved in water and toluene in a 50:50 ratioby volume. The yields of products in the two phases detected by HPLCanalysis are displayed in table 9. Analysis of the organic phaseindicated an absolute MAA yield of 3.42%, with no other productsdetected. The yield of MAA detected in the aqueous phase was 34.61%,therefore the partition coefficient for MAA between the toluene andaqueous phases=28.5 after cooling to ambient temperature. Thus thesolvent may be added to the aqueous phase before the decompositionperiod as well as after cooling.

TABLE 9 Detected in Detected in Aqueous Phase Toluene Phase Mass Balance54.83 0.00 Conversion 93.25 0.00 PY 3.62 0.00 CC 4.53 0.00 IC 0.76 0.00HIB 3.85 0.00 CM 0.00 0.00 MC 0.71 0.00 MAA 34.61 3.42 Key: - ICItaconic Acid MC Mesaconic Acid CC Citraconic Acid HIB HydroxyisobutyricAcid PY Pyruvic Acid

Examples 41-46 and Comp Ex 10

Solutions of a mixture of dibasic acids and methacrylic acid wereprepared in water containing 0.1M of each acid. Sodium hydroxide wasadded to each solution at a different concentration as shown in table10. The aqueous solution was extracted with an equal volume of tolueneat room temperature. The quantity in the organic and aqueous layers areshown in the table.

TABLE 10 water toluene [NaOH] [MAA] [CC] [IC] [MC] [MAA] [MAA] Comp 00.1 0.1 0.1 0.1 0.052 0.048 Ex 10 Ex 41 0.025 0.1 0.1 0.1 0.1 0.0480.052 Ex 42 0.05 0.1 0.1 0.1 0.1 0.050 0.050 Ex 43 0.075 0.1 0.1 0.1 0.10.052 0.048 Ex 44 0.1 0.1 0.1 0.1 0.1 0.051 0.049 Ex 45 0.125 0.1 0.10.1 0.1 0.050 0.050 Ex 46 0.15 0.1 0.1 0.1 0.1 0.051 0.049

In the presence of 0.3M of combined dicarboxylic acids, the addition ofbase has no effect on the concentration of MAA extracted. In fact, bycomparison with data in example 5, and table 5, it is obvious that theamount extracted was the same as for a solution free of dicarboxylicacid and base. This shows the effectiveness of the presence of thedicarboxylic acid in preventing the loss of organic solvent solubilityin the presence of base.

Comparative Example 11

Solutions of acrylic acid in water were extracted with toluene under thesame conditions as in comparative example 3 except that the acid waschanged from MAA to AA.

The starting concentrations and the quantity extracted into toluene areshown in table 11.

TABLE 11 Conc/M [organic]/M [aq]/M) Comp Ex 11a 1 0.20 0.80 Comp Ex 11b0.75 0.12 0.63 Comp Ex 11c 0.5 0.064 0.44 Comp Ex 11d 0.25 0.026 0.22Comp Ex 11e 0.125 0.0070 0.12 Comp Ex 11f 0.0625 0.0025 0.060 Comp Ex11g 0.0312 0.00098 0.030 Comp Ex 11h 0.0156 0.00052 0.015 Comp Ex 11j0.0078 0.00021 0.0076

The relative concentration between the aqueous and organic phases isplotted according to the equation[AA_(tol)]=K[AA_(aq)]²and shown in FIG. 5.

The excellent straight line fit has a much lower slope than for example3, indicating that AA much prefers the aqueous layer.

Comparative Example 12

In order to increase the solubility of the AA in the organic layer ahigher polarity is likely to be required. The extraction of a 0.1M aq AAsolution was studied with an equal volume of a mixture between tolueneand butanone.

% extracted % extracted % Butanone Maleic acid Acrylic acid 0 0 5.01 100.32 14.57 20 1.46 25.26 30 3.41 35.45 40 5.19 44.14 50 10.62 53.47 6010.77 57.31 70 15.01 63.39 80 19.88 67.47 90 27.09 70.04 100 34.32 65.56

There is a very large increase in the extent of extraction as thebutanone concentration increases, although the selectivity of extractionfalls. It is likely that a mixture containing sodium salts will show amuch improved separation between acrylic acid solubility and maleic acidsolubility and that an appropriate choice of solvent of intermediatepolarity will allow sufficiently effective a separation that the acrylicacid can be further purified by e.g. distillation.

Preparative Examples—Experiments Conducted Using the Flow Reaction Usethe Procedure as Outlined Below

Flow Reaction Procedure

A reactant feed solution was prepared comprising itaconic, citraconic,mesaconic acid or citramalic acid at a concentration of 0.5 M and sodiumhydroxide also at a concentration of 0.5 M. The itaconic acid used(>=99%) was obtained from Sigma Aldrich (Catalogue number: L2,920-4);citraconic acid (98+%) was obtained from Alfa Aesar (L044178); mesaconicacid (99%) was obtained from Sigma Aldrich (Catalogue number: 13,104-0).The citramalic acid solution is prepared by dissolving solid(R)-(−)-citramalic acid (commercially available from VWR International)with sodium hydroxide catalyst in nano-pure water to the requiredconcentration.

The deionised water used for solvation of the acids/NaOH was firstdegassed via sonication in an Ultrasound Bath (30 KHz) for a period of 5minutes.

This reactant feed solution was fed into the reactor system via a Gilson305 HPLC pump module fitted with a Gilson 10 SC pump head. The rate atwhich the reactant feed solution was pumped into the reactor systemdepended on the residence time required and the volume of the reactor.The feed rate was also dependent on the density of the reaction mediawhich in turn depended on the reaction temperature.

The reactant feed solution was pumped to the reactor via 1/16″ internaldiameter stainless steel (SS 316) pipe (Sandvik). The reactor consistedof a straight section of ½″ SS 316 pipe, encased in an aluminium blockfitted with two 800W Watlow heater cartridges. The transition of the SS316 piping from 1/16″ to ½″ was achieved with Swagelok SS 316 reducingunions and required an intermediate step of ⅛″ pipe (i.e. 1/16″ pipe to⅛″ pipe to ½″ pipe).

The volume of the reactor was calculated theoretically, and confirmedfrom the difference in weight when the reactor was filled with water andwhen it was dry; for the experiments described, the volume of thereactor was 19.4 cm³. After the ½″ pipe ‘reactor’, the piping wasreduced back down to 1/16″, before meeting a Swagelok SS 316 1/16″cross-piece. At this cross-piece, a thermocouple (type K) was used tomonitor the temperature of the exit feed.

Reactor volume (used for residence time) is defined as the volume of the½″ section of pipe between the two ½″ to ⅛″ reducers located immediatelybefore and after the aluminium block.

The product mixture is finally passed through a heat exchanger (a lengthof ⅛″ pipe within a ¼″ pipe through which cold water was passed incontra flow) and a manual Tescom Back-Pressure Regulator through whichback-pressure (pressure throughout the whole system between this pointand the pump head) was generated: the pressure employed was 3000 psi forall experiments described. Samples were collected in vials before beingprepared for analysis.

The required temperature for reaction was achieved using a thermostatfitted with a Gefran controller (800 P), which mediated power applied tothe two Watlow cartridge heaters. Each set of experiments involvedworking at a single temperature while varying residence time betweenruns. The required flow rate for the first run was set at the Gilsonpump module. The pump was then left for a period of around 20 minutes,pumping only deionised water, in order for the heat-transfer between thealuminium block to have become consistent. The heat-transfer was deemedto have achieved equilibrium when the temperature indicated by thethermocouple located at the reactor exit feed position did not change(accurate to 1° C.) for a period of more than 5 minutes. At this stagethe inlet of the pump was transferred from the container of deionisedwater to the container of the prepared reactant mixture. The totalvolume of the apparatus (including reactor) was approximately doublethat of the reactor itself; this was previously determinedexperimentally. For a particular flow rate, the reactant mixture wasleft pumping for approximately three times the required period for it tohave begun emerging from the final outlet, in order to ensure that asteady-state of reaction had been achieved. After this time a 20 mlsample of the apparatus exit solution was collected for analysis. Boththe rate of collection of the exit solution and the rate at which thereaction solution was consumed were recorded against time in order tomonitor the consistency of the pump efficiency. Following samplecollection from a particular run, the pump inlet was switched back tothe container of deionised water, and the flow rate was increased to itsmaximum for a period of approximately 10 minutes to ensure that allremaining material from the previous run had been purged from thesystem. This procedure was then repeated for the subsequent residencetime to be investigated.

Analysis

Quantitative analysis of products was achieved using an Agilent 1200series HPLC system equipped with a multi wave-length UV detector.Products were separated using a Phenomenex Rezex RHM monosaccharideH+(8%) column held at 75° C., protected by a guard column. The methodused was isocratic, implementing a 0.4 mlmin⁻¹ flow rate of aqueous0.005 M H₂SO₄ mobile phase. The compounds contained in product sampleswere found to have optimum UV absorbance at the shortest wavelengthcapable of the MWD detector of 210 nm (bandwidth 15 nm). All productcompounds were calibrated for their UV detection, by correlating theirUV absorbance against a range of concentrations. Linear response rangeswere determined for each compound, and the most compatible range ofconcentrations found for all compounds of interest was between 5×10⁻³ Mand 1×10⁻³ M. Thus, adequate quantitative detection of most products wasachieved with a 1 to 100 dilution of samples obtained from the apparatusbefore HPLC analysis (a dilution of 1 to 100 would mean that whenstarting with a 0.5 M reaction solution, any product generated in ayield of between 20%-100% would fall within the linear response range ofconcentrations). Where compounds fell outside this linear response range(e.g. a yield of less than 20%), a second HPLC analysis was conductedusing a dilution of 1 to 10. Any samples which were not accuratelyquantified using the 1 to 10 dilution method were considered to be tracein concentration and therefore negligible.

Procedure

The following procedure was carried out. The reagent mixture comprisingacid and sodium hydroxide was first prepared. The required flow rate toachieve the residence time was calculated using the reactor volume andthe density of water (calculated from temperature).

FIG. 6 shows a schematic representation of the apparatus for the presentinvention. Reaction solution 18 was located in receptacle 20 which wasconnected to inlet 16. The inlet was connected via conduit 22 to thereactant pump 2 which was operable to pump the solution 18 to thereactor tube 24 tube which was housed in a heater cartridge 26 whichextended circumferentially along the reactor 24 length. The conduit 22between the pump 2 and the reactor 24 proceeded from the pump via avalve 28 for operation control, pressure monitor 30 and pressure reliefvalve 32. In addition, a trip switch 34 was connected to the pressuremonitor 30, reactant pump 2 and a temperature monitor 14. Thetemperature monitor 14 was located in conduit 22 immediately afterreactor 24 and before outlet 6. In addition, after the monitor 14, theconduit proceeded to the outlet via a filter 36, heat exchanger 8 andback pressure regulator 4. At the outlet 6, the product was collected incollection receptacle 38.

The reactor 24 also included a temperature control unit 10, 12 tocontrol the temperature of the reactor 24. The apparatus also included aquenching system which includes a separate inlet 40 for quench water 44in quench water receptacle 42. The inlet 40 was connected to the outlet6 via conduit 46 which included a separate quench pump 48 followed by avalve 50 for control of the quench water. The quench water conduit 46met the reaction conduit 22 immediately after the temperature monitor 14of the reactor 24 and before filter 36 to quench any reaction after thereactor. The quench pump 48 and temperature controller unit 10, 12 werealso connected to trip switch 34 for necessary shut down when the tripcriteria are met.

The reactor pump 2 was turned on and deionised water was pumped into thesystem. The back pressure regulator 4 was gradually adjusted to therequired pressure (3000 psi).

The pump operation efficiency was checked at 5 ml min⁻¹ by recordingtime taken to collect a volume of 20 ml of water from system outlet6. >90% efficiency was acceptable.

The pump flow rate is then set to that required for the run.

The water supply (not shown) to the heat exchanger 8 was set to alow-moderate flow, depending on the reaction temperature and pump flowrate for the experiment.

The heater thermostat 10 fitted with a temperature controller 12 was setto the required temperature for the run.

Once the required temperature had been reached (as indicated bythermostat 10), reactor outlet temperature was monitored by the reactortemperature monitor 14 until the value (accurate to 1° C.) was observedto remain static for a period of at least 5 minutes (this usually tookapproximately 20 minutes).

The pump inlet 16 was switched from the deionised water container (notshown) to the prepared reagent mixture container 18 (this requiresstopping the pump flow for a few seconds). The initial volume of reagentmixture in container 18 was recorded.

Calculations can indicate the period before product solution will beginto emerge from the system outlet 6. However, in practice, this wasconfirmed by the visual and audible presence of gas bubbles exiting theapparatus (generated from the decomposition of reagents). This wasallowed to continue for a period that is ×3 the period taken for theproduct solution to emerge. This ensured that the product mixture ishomogenous.

At the outlet 6, 20 ml of product solution was collected and the timetaken for this collection was recorded. A final time and volume readingwas also taken for the reagent mixture.

After product collection, the pump inlet was transferred back to thedeionised water container, and the pump was set to “prime mode” (maximumflow rate) and left for a period of approximately 10 minutes.

The flow rate of the pump was then set to the required value for thesubsequent run.

Again the reactor outlet temperature was monitored and was consideredsteady when the value did not change for a period of at least 5 minutes(this usually took approximately 10 minutes).

This experimental method was repeated until all required runs for theexperiment had been performed.

After all runs had been completed, the deionised water was pumped intothe system with the pump on prime mode and the heater (thermostat) wasswitched off.

When the reactor outlet temperature had dropped below 80° C., the pumpwas switched off and the water supply to the heat exchanger was alsoceased.

Methacrylic Acid Extraction

Solutions prepared according to the preparative procedure above wereextracted with an equal volume of toluene. In the first set ofexperiments no extra acid was added. In the second set the acid used forthe original high temperature decomposition was added such that thetotal concentration of dicarboxylic acids (Itaconic, citraconic,mesaconic, Citramalic) plus 2-hydroxyisobutyric acid equalled 0.5M,which was the starting concentration for the original decomposition. Theresults in table 10 show that addition of acid has a very large impacton the amount extracted at the high concentrations of base present.

TABLE 10 Example Example Example Example Example 47 48 Example 49Example 50 51 52 53 Feed IC IC IC IC IC MC CC Original 0.5  0.5  0.5 0.5  0.5  0.5  0.5  Feed conc/M MAA 19.25%  64.73%  58.36%  56.74% 54.42%  44.89%  44.93%  ICA 16.35%  0.99% 0.84% 0.00% 0.16% 7.72% 5.88%Citramalic 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CCA 36.76%  1.69%0.50% 0.00% 0.26% 16.27%  12.40%  MCA 15.18%  2.08% 0.64% 0.08% 0.30%13.28%  9.93% HIB 11.26%  23.04%  22.12%  19.33%  13.07%  13.72% 14.25%  PY 0.36% 3.06% 2.69% 2.63% 2.67% 1.31% 1.77% CT 0.07% 0.91%0.74% 0.53% 0.63% 0.63% 0.65% Acids Mass 99.23%  96.50%  85.89%  79.31% 71.51%  97.82%  89.81%  Balance No added Acid % Extracted 11.55%  0.05%1.00% 0.00% 0.00% 7.02% 2.01% pH 4.87 6.65 >7    >8    >8    5.34 5.70Acid Added % Extracted 20.21%  29.43%  28.31%  28.04%  27.90%  30.56% 29.74%  pH 4.39 4.45 4.47 4.47 4.46 4.05 4.16

Comparative Example 12

The efficiency of MAA extraction into a mixture of 2-butanone ando-xylene in the ratio 75:25 was studied. The presence of xylene in thisorganic mixture partly restricts the solubility of butanone in theaqueous phase, which is a significant issue where butanone is used aloneas the organic phase; at this particular ratio, the distributioncoefficient for MAA is reported to be a maximum of approximatelyK=7.00.²³ In this case it was found that roughly 80% of MAA wasextracted into the organic phase, which appeared extremely desirable;however, other dicarboxylic acids concerned in the decompositionexperiments (i.e. IC, CC etc.) also showed a slight affinity to theorganic phase of up to 11%.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

The invention claimed is:
 1. A process for the continuous production of(meth)acrylic acid comprising the steps of: forming an aqueous medium ofat least one base catalyst and at least one dicarboxylic acid and/or aprecursor thereof, wherein the at least one dicarboxylic acid isselected from fumaric, maleic, malic, itaconic, citraconic, mesaconic orcitramalic acid or mixtures thereof; decarboxylating the at least onedicarboxylic acid in the presence of the at least one base catalystunder suitable conditions of temperature and pressure to produce(meth)acrylic acid and/or base salts thereof in the aqueous medium;introducing an organic solvent to the said aqueous medium for solventextraction of the (meth)acrylic acid into an organic phase; wherein thedicarboxylic acid and/or pre-cursor thereof forms a first acid salt anda second acid salt thereof in the presence of the base catalyst;characterised in that the level of base catalyst to the said at leastone dicarboxylic acid and/or pre-cursor thereof is maintained at asub-stoichiometric level in relation to the formation of the first acidsalt of the at least one dicarboxylic acid and/or pre-cursor thereofduring the extraction process.
 2. The process according to claim 1,wherein the concentration of (meth)acrylic acid in the aqueous phaseextraction is at least 0.05 mol dm⁻³.
 3. The process according to claim1, further comprising the additional step of adding an additional amountof at least one of the dicarboxylic acids and/or a pre-cursor thereof tothe aqueous reaction medium to enhance the solvent extraction of the(meth)acrylic acid into the organic phase.
 4. The process according toclaim 1, wherein the dicarboxylic acid and/or a pre-cursor thereof isselected from a group consisting of citric, itaconic, citramalic,citraconic and mesaconic acid or mixtures thereof.
 5. The processaccording to claim 4, wherein the dicarboxylic acid and/or a pre-cursorthereof is selected from a group consisting of citric, itaconic,citramalic and citraconic acid or mixtures thereof.
 6. The processaccording to claim 1, wherein the dicarboxylic acid is selected from agroup consisting of maleic, fumaric, and malic acid or mixtures thereof.7. The process according to claim 1, wherein the dicarboxylic acid ismalic acid.
 8. The process according to claim 1, wherein in the case ofthe (meth)acrylic acid being methacrylic acid, the organic solvent is anexternal organic solvent with respect to the reaction medium.
 9. Theprocess according to claim 1, wherein the dicarboxylic acid is selectedfrom citramalic or itaconic acid.
 10. The process according to claim 1,wherein the organic solvent for (meth)acrylic acid extraction isselected from hydrocarbon solvents or oxygenated solvents.
 11. Theprocess according to claim 10, wherein the hydrocarbon solvents areC₄-C₂₀ hydrocarbon solvents.
 12. The process according to claim 10,wherein the organic solvent include toluene, benzene, ethylbenzene,xylene, trimethylbenzene, octane, heptane, hexane, pentane,cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclohexene,methylcyclohexane, methylethylketone, methyl methacrylate, mixturesthereof; and ionic liquids which are immiscible with water.
 13. Theprocess according to claim 1, wherein the mixture of solvents for theextraction of (meth)acrylic acid is a C₄-C₂₀ hydrocarbon solvent andmethyl methacrylate.
 14. The process according to claim 1, furthercomprising the step of separating the organic phase from the aqueousphase after extraction followed by subsequent treatment of the organicphase to isolate the (meth)acrylic acid extracted in the extractionprocess from the organic solvent.
 15. The process according to claim 1,wherein the organic solvent is introduced to the aqueous medium beforeor after decarboxylation.
 16. The process according to claim 1, whereinthe sub-stoichiometric level of base is maintained, after, if necessary,being implemented post reaction, during at least that part of theextraction process which is carried out after the decarboxylation step.17. The process according to claim 1, wherein the sub-stoichiometriclevel of base is maintained throughout the reaction and extraction. 18.A method of preparing polymers or copolymers of (meth)acrylic acid or(meth)acrylic acid esters, comprising the steps of: (i) preparation of(meth)acrylic acid in accordance with claim 1; (ii) optionalesterification of the (meth)acrylic acid prepared in (i) to produce the(meth)acrylic acid ester; (iii) polymerisation of the (meth)acrylic acidprepared in (i) and/or the ester prepared in (ii), optionally with oneor more comonomers, to produce polymers or copolymers thereof. 19.Polyacrylic acid, polymethacrylic acid, polyalkylacrylate,polymethylmethacrylate (PMMA) and polybutylmethacrylate homopolymers orcopolymers formed from the method of claim
 18. 20. The process for theproduction of methacrylic acid comprising: providing a source of apre-cursor acid selected from aconitic, citric and/or isocitric acid;performing a decarboxylation and, if necessary, a dehydration step onthe source of pre-cursor acid by exposing the source thereof in thepresence or absence of a base catalyst to a sufficiently hightemperature to provide a dicarboxylic acid selected from itaconic,mesaconic, citraconic and/or citramalic acid; and using the dicarboxylicacid produced in a process according to claim 1.